Change how PHINodes store their operands.

Change PHINodes to store simple pointers to their incoming basic blocks,
instead of full-blown Uses.

Note that this loses an optimization in SplitCriticalEdge(), because we
can no longer walk the use list of a BasicBlock to find phi nodes. See
the comment I removed starting "However, the foreach loop is slow for
blocks with lots of predecessors".

Extend replaceAllUsesWith() on a BasicBlock to also update any phi
nodes in the block's successors. This mimics what would have happened
when PHINodes were proper Users of their incoming blocks. (Note that
this only works if OldBB->replaceAllUsesWith(NewBB) is called when
OldBB still has a terminator instruction, so it still has some
successors.)

llvm-svn: 133435

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 92464e8cf13..b4f74f97e97 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -153,13 +153,13 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P) {
   // Delete the unconditional branch from the predecessor...
   PredBB->getInstList().pop_back();
   
-  // Move all definitions in the successor to the predecessor...
-  PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
-  
   // Make all PHI nodes that referred to BB now refer to Pred as their
   // source...
   BB->replaceAllUsesWith(PredBB);
   
+  // Move all definitions in the successor to the predecessor...
+  PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
+  
   // Inherit predecessors name if it exists.
   if (!PredBB->hasName())
     PredBB->takeName(BB);